Use a good guitar in a good room, know how to play it properly, know your song backwards, how to sing it properly, have a good mic in an appropriate location relative to the guitar and room and then the voice and the room, understand what post processing you'd like to do (if any) and what tracking / mix options you'd like to have. Capture the performance/s then mix them together and you're done.
Simple really.
After that, come back on here and tell us it's not loud enough and we'll deal with that separately...
And to the second question... see previous reply and, you can use the same mic for both, depending upon what it is. Over time, you will have more than one mic, however.
Oh, and learn to sing and play separately, if you can't already... it opens up your options just a tad...
Tip - record something, then decide what needs to be improved. Ask for help here if you don't know. You're just in theory land at the moment. Theory is good in theory, but not so much in practice.
All clear? Good - o. Welcome aboard the good ship HR, where vague questions asked, get vague answers in return..
... and there's whole threads about recording acoustic guitars here already. Find them. Read them.
